#Define a procedure is_palindrome, that takes as input a string, and returns a
#Boolean indicating if the input string is a palindrome.

#Base Case: '' => True
#Recursive Case: if first and last characters don't match => False
#if they do match, is middle palindrome?

def is_palindrome(s):
    if s == '':
        return True
    else:
        if s[0] == s[-1]:
            return is_palindrome( s[1:-1] )
        else:
            return False

print is_palindrome('')
#>>> True
print is_palindrome('abab')
#>>> False
print is_palindrome('abba')
#>>> True
